It is common to equip vehicles with a motor-driven fluid compressor having a governor device in which the motor is stopped and started by a fluid pressure operated electric power control switch device which is responsive to the fluid pressure in the main or storage reservoir. In practice, the fluid pressure operated control switch includes a pressure operated piston to cause the electric switch contact members to move to an open position to thereby deenergize the motor and stop the compressor.
When the fluid pressure in the reservoir is reduced to a predetermined level, the usual high pressure valve of the governor is seated and the fluid pressure in the piston chamber is vented to atmosphere. The switch operating piston is spring biased to restore the switch contact members to their closed position, thereby starting the compressor motor and continuing operation of the compressor until the fluid pressure has built up in the reservoir, at which time the governor operates in a well-known manner to supply fluid under pressure to the aforementioned piston chamber to act on the one side of the piston to cause the switch contact members to move to their open position as above mentioned.
In the past, the air governor portion included a pair of reciprocating spool valves having metal-to-metal valve seats which are prone to leakage and seizure. It has been found with such governors that dirt and other foreign material in the high pressure valve chamber causes improper opening of the high pressure valve such that the fluid pressure is delivered to the piston chamber of the control switch at a dramatically reduced rate to cause slow opening of the contact members thereof. Another possible adverse effect of dirt and debris present in the high pressure valve is the improper seating of the high pressure valve, resulting in leakage of fluid under pressure past the valve and seat to the piston chamber of the control switch to cause a slow undesired fluid pressure build-up which in turn causes a slow undesired opening of the electrical switch contact members. The slow movement of the control piston caused by the improper seating or opening of the high pressure valve of the governor correspondingly results in slow opening of the electrical switch contact members, causing excessive arcing and burning of the main contacts to cause failure and to thereby result in the inability to complete the compressor motor supply circuitry when fluid pressure in the reservoir is low.
Recently, there has been a rash of such problems which has resulted in the need to structurally redesign the governor portion to improve the functional operation of the electrical switch contact controller to effectively energize and deenergize the electric drive motor.